CA1168213A - Polymerisation catalyst - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A supported Ziegler catalyst prepared by the following steps:
(A) heating together at a temperature in the range 250 to 1100°C a refractory oxide support material having surface hydroxyl groups and one or more halogen-free metal derivatives which are hydrides and/or organic derlvatives of the metal.
(B) reacting the product from (A) with one or more organometallic compounds having the feneral formula MRIaQb-a wherein M is a metal atom, R1 is a hydrocarbon group, Q is a halogen or an oxyhdrocarbyl group, b is the valency of M and a is an integer from 1 to b and wherein the metal atom M is aluminium, boron, lithium, zinc or magnesium, (C) impregnating the solid protuct from step (B) with one or more halogen-containing transition metal compounds wherein the transition metal or metals comprise titsnium and/or vanadium and/or zirconium.

Description

50~2 POLYMERISATION CATALYST

The present invention relates to a supported Ziegler catalyst for polymerising l-olefins and to a process for polymerising l-olefins employing the catalyst.
It has long been known that l-olefins such as ethylene can be polymerised by contacting them under polymerisation conditions with a catalyst obtained by activating a transition metal-containing component, e.g. a titanium compound such as titanium tetrachloride, with an activator or co-catalyst, e.g. an organo-metallic compound 3uch as triethylaluminium. Catalysts comprising the transition metal-10 containing component and the co-catalyst or activator are generally referred to in the art as "Ziegler catalysts" and this terminology will be used throughout this specification.
The Ziegler catalyst component comprising the transition metal can be used either in an unsupported condition, or supported on 15 support materials such as silicon carbide, calcium phosphatej silica, magnesium carbonate `and sodium carbonate.
UK Patent Specification No. 1,256,851 discloses a catalyst for ~; the low-pressure polymerisation and copolymerisation of olefins, comprising:
(a) an organometallic compound, or an organosilicon compound having at least one Si-H bond, and (b) a solid product obtained by reacting a substantially -~ anhydrous support consisting of a solid bivalent-metal compound with an organometallic compound, or an organosilicon compound 25 having at least one Si-H bond, this being either identical to or ' 1 J ~
.: ;., , ~ .

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different from "(a)", separating the solid product resulting from the reaction, reacting this pcoduct with a halogenated derivative of a transition metal, and separating the final solid reaction product;
the molar ratio of "(a)" to the transition metal chemically bonded to the support being at least 2.
UK Patent 1,306,044 relates inter alia to a process for polymerising alpha-olefins using a catalyst comprising an organometallic compound and the solid product obtained by reacting silica or alumina with an excess of a compound of the formula MRnX wherein M is aluminium or magnesium, R is a hydrocarbon radical, X is hydrogen or halogen, m is the valency of M and n is a whole number not greater than m, separating and washing the solid product and reacting it with an excess of a halogen-containing transition metal compound and separating the solid reaction product.
It is an object of the present invention to provide an improved supported Ziegler catalyst.
Accordingly the present invention provides a supported Ziegler catalyst prepared by the following steps:
(A) heating together at a te~,perature in the range 250 to 1100 C
a refractory oxide support material having surface hydroxyl groups and one or more halogen-free metal derivatives which are hydrides and~or organic derivatives of the metal, (B) ~eacting the product from step ~A) with one or more organometallic compounds having the general formula MR a Q b a wherein M is the a metal atom~ Rl is a hydrocarbyl group, Q is halogen or an oxyhydrocarbyl group, b is the valency of M and a is an integer from 1 to b and wherein the metal is aluminium, boron, lithium, zinc or magnesium, (C) impregnating the solid product from step (B) with one or more halogen-con~aining transition metal compounds wherein the transition metal or metals comprise titanium and/or vanadium, and/or zirconium.
Throughoutthis specification silicon and boron are regarded as metals.
In step A the refractory oxide support material is suitably any

2:13 particulate oxide or mixed oxide, e.g. silica, silica-alumina, alumina, zirconia, thoria, titania or magnesia, having surface hydroxyl groups capable of reacting with the halogen free metal derivative Preferred support materials are those suitable for use in the S well known Phillips process for the polymerisation of ethylene (see for example UK Patent Specifications 790, 195; 804,641;
853,414; French Patent Nos. 2,015,128; 1,015,130 and Belgian Patent No. 741,437). Microspheroidal silicas and silica-aluminas having a mean particle diameter in the range 30 to 300 ~m, a surfaee 10 area of 50 to 1000 square metres per gram and a pore volume of 0.5 to 3.5 cc/gram are particularly preferred.
The metal in the halogen-free metal derivative is suitably selected from titanium, al~minium, nickel, vanadium, zirconium, boron~ magnesium, silicon, zinc or tin.
me halogen-free metal derivative contains one or more hydride "atoms" and/or one or more organic groups. By an organic group is meant a group containing at least carbon and hydrogen, optionally concaining oxygen and/or nitrogen. Examples of suitable organic groups are alkyl, aryl, alkenyl, alkoxy, aryloxy, carboxylate or alkyl-20 amino. The organic group can be mono- or poly-valent. ~xamples of halogen-free metal derivatives are titanium tetraisopropylate~
titaniùm acetylacetonate~ titanocéne diacetate~ triethylaluminium~
diethylalul~inium hydride~ dibutylaluminium hydride~ aluminium isopropylate~ nickel acetate~ nickél acetylacetonate, nickelocene 25 vanadylethylate (VOEt3), vanadyl isopropylate, zircc~nium tetraiso-propylate, zirconium tetrabutylate, triethyl boron, triethyl borate, magnesium diethylate, dibutyl magnesium, tetraethyl silicate, diethyl zinc, tributyl tin hydride and butyl octyl magnesium.
me c~uantity of halogen-free metal derivative employed in step 30 (A) of the present invention is suitably 0.005 to 2.0 moles, preferably 0.1 to 0.5 moles based on the number of moles of hydroxyl groups present in the refractory oxide support material.
If the halogen-free metal derivative reacts with water, it is preferred to dry the refractory oxide support material prior to the 35 performance of step (A) of the present invention and to carry out step (A) under substantially anhydrous conditions.

The refractory oxide support material and the halogen-free metal derivative are brought together in step A of the present invention in any desired manner. If the halogen-free metal derivative is a solid it is preferred to dissolve the solid in a suitable inert liquid diluent and to mix the solution with the refractory oxide and evaporate the diluent prior to or during the heating in step A.
The heating in step A is carried ~ut at a temperature in the range 250 to 1100C, preferably 400 to 900C. The heating may be continu~d as long as desired but is preferably carried out for a length o~ tim-within the range 30 minutes to 24 hours. The heating may be carri~dout, for example, in vacuo, in an inert gas atmosphere (e.g. nitrogen or argon), or in air. Preferably the mixture of refractory oxide support material and halogen-free metal derivative are fluidised by inert gas or air during the heating in step A.
The product from step A in the present invention is then reacted with the organometallic compound defined in step B. The organo-metallic compound must contain at least one metal-carbon bond.
Preferred organometallic compounds are trihydrocarbyl aluminium, tri-hydrocarbyl boron, dihydrocarbyl zinc or magnesium and hydrocarbvl lithium c~mpounds. Examples of organometallic compounds which can be employed-are triethyl aluminium, isoprenyl aluminium, diethyl aluminium chloride, diethyl aluminium ethoxide, triethyl boron, dibutyl magnesium, ethyl magnesium bromide, diethyl zinc and butyl lithium. Aluminium tri-alkyls are particularly preferred, especially those containing 1 to 10 carbon atoms in each alkyl group.
The quantity of organometallic compound employed in step B is suitably in the range 0.1 to 10.0 moles, preferably 0.5 to 1.5 moles per mole of surface hydroxyl groups on the original refactory oxide support material.

3~ The reaction between the organometallic compound and the product from step A can be conducted in any desired manner provided that the reaction mixture is substantially free from water and other impurities containing reactive groups which react with the organometallic compound.
The reaction can be conducted in the present of an inert diluent or solvent for the organometallic compound if desired. Examples of suitable solvents are liquid hydrocarbons, for example, cyclohexane or normal-hexane. The reaction is preferably carried out in a solvent at a temperature between ambient and the boiling point of the solvent, for example at a temperature in the range 10-80C~
although temperatures above or below this range can be employed if desired. The reaction between the organometallic compound and the product from step A generally occurs rapidly at ambient temperature and a reaction time of one hour or less is normally adequate although longer times can be employed if desired.
After the reaction between the organometallic compound and the product from step A is substantially complete, the unadsorbed organometallic compound, if any, can be separated from the solid product from step B if desired. The separation can be acnieved, for example, by washing the solid product with an anhydrous inert solvent, for example, cyclohexane, normal-hexane or petroleum ether. The solid product must be protected from contact with other substances ~ith ~hich it may deleteriously react, for example air.
In step C the solid product is impregnated with one or more halogen-containing transition metal compounds wherein the transition metal or metals comprise titanium, vanadium or zirconium.
The titanium or zirconium is preferably tetravalent and the vanadium is preferably tetra- or penta-valent. Preferably these compounds are selected from compounds having the general formulae DY, DOY( 2) and D(OR )sY wherein D is the titanium, vanadium or zirconium; Y is halogen, preferably chlorine; 0 is oxygen; R is a hydrocarbyl group, for example alkyl, aryl or cycloalkyl preferably containing 1-10 carbon atoms; p is the valency of D; and s is an integer from 1 to p-l.
Examples of suitable titanium compounds are titanium tetrachloride t trichlorotitanium ethylate, dichlorotitanium diisopropylate and titanium oxychloride. Examples of suitable vanadium compounds are vanadyl chloride and vanadium tetrachloride. Examples of suitable zirconium compounds are zirconium tetrachloride and zirconyl chloride.
Titanium tetrachloride and vanadyl chloride or mixtures thereof are preferred.
The quantity of transition metal compound employed in preparing the catalyst of the present invention is suitably 0.05 to 10 moles, preferably 0.1 to 1.5 moles, most preferably 0.4 to l.0 moles ?er mole of hydroxyl groups in the original support material. When a mixture of titanium and vanadium compounds is employed in step C of the present invention, preferably the atomic ratio of Ti:V used in the catalyst preparation is in the range 100:1 to 1:100, most preferably 10:1 to 1:10~
The impregnation can be carried out using the neat (undiluted) transition metal compounds or by dissolving the transition metal compound(s) in an inert solvent, for example a liquid hydrocarbon solvent. The inert solvent when used must be free from functional groups capable of reacting with the solid material obtained from step B and the transition metal compound(s). Cyclohexane is an example of a suitable inert solvent. The impregnation step is preferably carried out by contacting the solid material obtained from step B with the transition metal compound(s) at a temperature in the range 10 to 50C.
It is particularly preferred to carry out the impregnation by stirring the mixture of said solid material and transition metal compound(s) in an inert solvent at a temperature in the range 10 to 30C. The contacting in the impregnation step C is preferably carried out for a time in the range 10 minutes to 24 hours.
The catalyst obtained from step C is preferably separated from any un~bsorbed transition metal compound by conventional means, for example, washing with dry inert solvent, or, if volatile transition metal compound(s) have been employed, by purging with inert gas, e.g. nitrogen, helium or argon. Preferably the separation is carried out by washing the catalyst several times with aliquots of dry hydrocarbon solvent.
The catalyst may be stored as the dry material in a suitable non-. reactive atmosphere, e.g. argon, nitrogen or other inert gas, or as a slurry in inert solvent.
The present invention further comprises a process for polymerisingone or more l-olefins comprising contacting the monomer under poly-merisation conditions with the catalyst of the present invention, preferably in the presence of a Ziegler catalyst activator. Ziegler catalyst activators and the methods in which they are used to activctte ~iegler cataly ts are well know~ iegler catalyst ac~ivators are organome~clllic deriv.ltives or hydrides of metals of Grolll>s ~.~ Il, LlI, ~ d l`V o1 ~ e ~ riodic Tal~l~ . P~lt-ti~-ularly preferre~ re trialkyl alumirlium ~ompouTIds or alkylalumlrlium halides, for example triethylaluminium, tributylaluminium and diethy~aluminium chloride. When a Ziegler catalyst activator is employed, preferably it is present in an amount such that the atomic ratio of metal atoms in the activator: total transition metal supported on the catalyst support is not greater than 10:1.
The polymerisation process of the present invention can be applied to the homopolymerisation of l-olefins, e.g. ethylene or propylene, or to the copolymerisation of mixtures of l-olefins, e.g. ethylene with propylene, l-butene, l-pentene, l-hexene,

4-methylpentene-1, 1,3-butadiene or isoprene. The process is particularly suitable for the homopolymerisation of ethylene or the copolymerisation of ethylene with up to 40% weight (based on total monomer) of comonomers.
The polymerisation conditions can be in accordance witn knowl-techniques used in supported Ziegler polymerisation. The poly-merisation can be carried out in the gaseous phase or in the presence of a dispersion medium in which the monomer is soluble. As a liquid dispersion medium, use can be made of an inert hydrocarbon which is liquid under the polymerisation conditions; or of the monomer or monomers themselves maintained in the liquid state under their saturation pressure. The polymerisation can if desired be carried out in the presence of hydrogen gas or other chain transfer agent to vary the molecular weight of the produced polymer.
The polymerisation is preferably carried out under conditions such that the polymer is formed as solid particles suspended irl a liquid diluent. Generally the diluent is selected from paraffins and cycloparaffins having from 3-30 carbon atoms per molecule.
Suitable diluents include for example isopentane, isobutane, and cyclohexane. Isobutane is preférred.
Methods of recovering the product polyolefin are well known in the art.

li~il~213 The polymerisation catalys~ of the preserlt invention can be used to make high density etllylene polymers and copolymers at high productivity having properties which render them s~table for a variety of applications. The catalyst exhibits good hydrogen sensitivity, i.e. the melt index of the produced polyolefins can be varied widely by employing hydrogen at different concentrations as chain transfer agent in the polymerisation process.
The invention is further illustrated by the following ~xamples.
In the Examples the melt index (MI2 16) and high load melt index (MI21 6) were determined according to ASTM method D 1238 conditions E and F respectively; the units are grams per lO
minutes.
Kd is a numerical measure of the molecular weight distribution of the polymer and is determined by a method similar to that disclosed in Sabia, R., J. Appl. Polymer Sci., 1963, 7, 347.
Example 1 Catalyst Preparation In step A of the catalyst preparation, silica (Davison 951 grade, 359) was slurried in petroleum ether (40-60C boiling range, 250 ml) in a nitrogen purged flask and titanium tetraisopropylate (10.6 ml) added. Stirring was continued for 1 hour after which the petroleum ether was removed on - a rotary evaporator. The dried support was heated at 750C in a bed fluidised with air for 5 hours. In step B, 10g of the resulLing material, which contained 6.0% titanium by weight, were stirred in dry cyclohexane (150 ml) in a nitrogen purged flask. Triethylaluminium (10% w~w solution in hexane, 43 ml, 3.09) was added dropwise, with stirring. Stirring was continued for 90 min after the addition was complete. The suspension was allowed to settle, the supernatant liquor decanted off, and fresh dry cyclohexane (150 ml) added. In step C, a mixture of titanium tetrachloride (1.08g) and vanadium oxytri-chloride (1.259) in dry cyclohexane (60 ml) was added dropwise, with stirring, to the reaction vessel. Stirring was continued for 90 min after the addition was complete. The catalyst was allowed to settle, the supernatant liquor decanted off, and the volume made llt;~Zi3 up to ca. 350 ml with fresh dry cyclohexane. The catalyst was used as a slurry and stored under nitrogen. A sample of the catalys-was dried and found by elementary analysis to contain 3.4% Al,

5.4% Ti, 2.3% V and 9.5% Cl.
Polymerisation Polymerisation was carried out in a 2.3 litre capacity stainless steel stirred autoclave. The reactor was purged with dry nitrogen, baked for 2 hours at 110C and then cooled to 75C. The catalyst slurry (118 mg dry weight) was added to the reactor using a syringe. Triethyl aluminium (0.5 ml of a 10%
weight/weight solution of AlEt3 in hexane) was added to improve the catalyst activity, together with isobutane (1 litre). The vessel was reheated to 90C and hydrogen (6.9 bar) was introduced.
Then ethylene was introduced to bring the total pressure in the reactor to 41.4 bar, and further ethylene was introduced throughout the duration of the polymerisation to maintain the pressure at 41.4 bar. The polymerisation temperature was 90C.
At the end of the polymerisation (about 1 hour) the diluent and unreacted ethylene were vented of and the polyethylene powder recovered. The polyethylene yield was 348g and the catalyst activity 2950 kg/kg/hour. The polyethylene was washed with acetone and treated with conventional stabilizer and the properties measured using standard procedures. The polymer properties were as follows M12,16 was l.Og/10 minutes, M121 6 was 34.7 g/10 minutes, Kd was 2.4. Screening through standard sieves showed that the polymer only contained 0.7 wt % of particles below 106 ~m.
Exam~le 2 Silica (Davison 952 Grade~ 40g) was suspended in a solution of al~minium isopropoxide (l5.lg) in toluene (500ml) and the mixture heated under reflux~ with stirring~ for 2~ hours. The solvent was removed on a rotary evaporator and the dried powder calcined for 2 hours at 500C in a bed fluidised with air. The support - material was cooled in a flow of dry nitrogen and stored under nitrogen prior to use. A portion of this material was used in the remaining catalyst preparation steps (steps 'B' and 'C'); these :, , lltiS~13 were carried out in the same manner as described in ~xample 1, except that the catalyst was washed with cyclohexane (250ml) before finally being made up with cyclohexane. The quantities of the reagents used are shown in Table 1.
PolYmerisation Polymerisation was carried out as described in Example 1.
Polymerisation results and polymer properties are summarised in Table 2.
Example 3 Silica (Davison 952 Grade, 40g) was suspended in a solution of nickel acetate (8.47g) in ethanol (300ml) and the mixture stirred for 15 min. The solvent was removed on a rotary evaporator ~nd the dried powder calcined for 1 hour at 550C in a bed fluidised with air. The support material was cooled in a flow of dry nitrogen and stored under nitrogen prior to use. Analysis of the support material sh~ed it to contain 4.7% Ni by weight. A portion of this material wa~ used in the remaining catalyst preparation steps (steps 'Bl and 'C'); these were carried out in the same manner as described in Example 1~ except that the alkylated support was 2C washed with cyclohexane ~250ml) after decantation (end of step 'B') and the catalyst was washed twice with cyclohexane (250ml each time) after decantation (end of step 'C'). The quantities of reagents used and the analysis of the dried catalyst are shown in Table 1.
Pol~merisation Polymerisation was carried out as described in Example 1.
Polymerisation results and polymer properties are summarised in Table 2.

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Claims (21)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A supported Ziegler catalyst prepared by the following steps:
(A) heating together at a temperature in the range 250 to 1100 C a refractory oxide support material having surface hydroxyl groups and one or more halogen-free metal derivatives which are hydrides and/or organic derivatives of the metal;
(B) reacting the product from (A) with one or more organometallic compounds having the general formula MR1 aQb-a wherein M is a metal atom, R 1 is a hydrocarbon group, Q is halogen or an oxyhydrocarbyl group, b is the valency of M and a is an integer from 1 to b and wherein the metal atom M is aluminium, boron, lithium, zinc or magnesium;
(C) impregnating the solid product from step (B) with one or more halogen-containing transition metal compounds wherein the transition metal or metals comprise titanium and/or vanadium and/or zirconium.

2. A catalyst as claimed in claim 1 wherein the metal in the halogen-free metal derivative employed in step (A) is selected from titanium, aluminium, nickel, vanadium, zirconium, boron, magnesium, silicon, zinc and tin.

3. A catalyst as claimed in claim 1 wherein the refractory oxide support material is silica, silica-alumina, alumina, zirconia, thoria, titania or magnesia.

4. A catalyst as claimed in claim 3 wherein the refractory oxide support material is silica or silica-alumina having a mean particle diameter in the range 30 to 300 µm.

5. A catalyst as claimed in claim 1, 2 or 3 wherein the halogen-free metal derivative employed in step (A) contains one or more hydride atoms.

6. A catalyst as claimed in claim 1, 2 or 3 wherein the halogen-free metal derivative contains one or more organic groups selected from alkyl, aryl, alkenyl, alkoxy, aryloxy, carboxylate and alkylamino groups.

7. A catalyst as claimed in claim 1, 2 or 3 where the quantity of halogen-free metal compound employed in step (A) is 0.1 to 0.5 moles per mole of hydroxyl groups present in the refractory oxide support material.

8. A catalyst as claimed in claim 1, 2 or 3 wherein the heating in step (A) is carried out at a temperature in the range 400 to 900 C.

9. A catalyst as claimed in claim 1, 2 or 3 wherein the organometallic compound employed in step (B) is an aluminium trialkyl.

10. A catalyst as claimed in claim 1, 2 or 3 wherein the quantity of organ-ometallic compound employed in step (B) is in the range 0.5 to 1.5 moles per mole of surface hydroxyl groups present on the original refractory oxide support material.

11. A catalyst as claimed in claim 1, 2 or 3 wherein the transition metal compound employed in step (C) is titanium tetrachloride, vanadyl chloride or a mixture thereof.

12. A catalyst as claimed in claim 1, 2 or 3 wherein the quantity of trans-ition metal compound employed in step (C) is in the range 0.1 to 1.5 moles per mole of hydroxyl groups present in the original support material.

13. A catalyst as claimed in claim 1, 2 or 3 wherein the transition metal compound comprises a mixture of titanium and vanadium compounds.

14. A catalyst as claimed in claim 1, 2 or 3 to which there is added a Ziegler catalyst activator.

15. A catalyst as claimed in claim 1, 2 or 3 to which there is added a trialkyl aluminium compound or an alkyl aluminium halide as Ziegler catalyst activator.

16. A process for polymerizing one or more 1-olefins comprising contacting the monomer under polymerization conditions with the catalyst claimed in claim 1, 2 or 3.

17. A process for polymerizing one or more 1-olefins comprising contacting the monomer under polymerization conditions with the catalyst claimed in claim 1, 2 or 3 and in the presence of a Ziegler catalyst activator.

18. A process for polymerizing one or more 1-olefins comprising contacting the monomer under polymerization conditions with the catalyst claimed in claim 1, 2 or 3 and in the presence of trialkylaluminium as Ziegler catalyst activator.

19. A process for homopolymerizing ethylene or copolymerizing a mixture of ethylene with up to 40% by weight of comonomer 1-olefins (based on total monomer) by contacting the monomer(s) with the catalyst claimed in claim 1, 2 or 3.

20. A process for homopolymerizing ethylene or copolymerizing a mixture of ethylene with up to 40% by weight of comonomer 1-olefins (based on total monomer) by contacting the monomer(s) with the catalyst claimed in claim 1, 2 or 3 and in the presence of a Ziegler catalyst activator.

21. A process for homopolymerizing ethylene or copolymerizing a mixture of ethylene with up to 40% by weight of comonomer 1-olefins (based on total monomer) by contacting the monomer(s) with the catalyst claimed in claim 1, 2 or 3 and in the presence of trialkylaluminium as Ziegler catalyst activator.